This application is based on Patent Application No. 2000-89652 filed Mar. 28, 2000 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet print head, an ink jet printing apparatus having the ink jet print head, and an ink jet printing method, and more specifically to a control for driving an energy generation element provided in each of a plurality of ink ejection nozzles in the ink jet print head.
2. Description of the Related Art
An on-demand type ink jet printing system is showing a rapid growth in recent years. A so-called bubble jet printing system in particular has found a wide range of applications because of its advantages, such as a simple structure of the print head and its capability of having a large number of nozzles arranged in high density. The print head using this bubble jet printing system employs a heater as the energy generation element for ejecting ink, which heats ink to generate a bubble and eject ink by the bubble energy.
In performing high-speed printing by using such a bubble jet printing system, it is effective to increase the number of nozzles. Driving many nozzles at the same time, however, causes a large power to be supplied to these nozzles instantaneously, giving rise to a possibility of a power supply voltage drop. Hence, to reliably operate a large number of nozzles, a power supply with a large capacity is required. In the bubble jet printing system, a bubble is generated in the ink by an electric power pulse of a very short duration as small as a few microseconds. Thus, when a large number of nozzles are driven at the same time, a large current flows at the instant of nozzle operation, causing a significant drop in the supply voltage. This results in a shortage of energy for nozzle operation, rendering the ink ejection from the nozzles unstable, significantly reducing the quality of a printed image.
To avoid this problem, it has generally been known to divide a large number of nozzles into a plurality of blocks and drive these blocks at different timings in a time-division manner. In this case, too, when an overall number of nozzles in the print head is large and each block is allocated with many nozzles, a significant voltage drop will occur whenever a block is driven. If the number of blocks is increased to reduce the number of nozzles to be operated at the same time, the time taken to drive all the blocks becomes long, making it necessary to reduce a drive frequency, which in turn leads to a reduced operation speed, another serious problem directly involved with the printing performance.
As a common countermeasure to eliminate such a voltage drop in a field other than the printing technology field, a remote sensing system has been known. This system detects a voltage between terminals of each load that consumes electricity, and feeds back the detected voltage to a constant voltage circuit of the power supply to keep the voltage across the load constant and thereby stabilize the operation of the load. However, in an attempt to apply such technology to a bubble jet printing system, the remote sensing system may not work effectively because the drive pulse is very short. That is, for a pulse current of a very short pulse width to be fed back, a high-speed feedback circuit is required. But because the remote sensing circuit has long wiring, the current phase is delayed making the high-speed feedback circuit operation unstable, causing an oscillation problem.
To solve this problem, Japanese Patent Application Laid-open No. 10-181017 (1998) previously filed by the applicant of this invention describes a drive method which counts the number of nozzles to be driven at the same time and determines a pulse width of a voltage pulse based on the count value. Because this drive method estimates a voltage drop of voltage applied to the heater of the nozzle and, based on the estimated result, corrects the drive pulse width, it is possible to perform a stable drive without applying an excess voltage. However, in the drive system of Japanese Patent Application Laid-open No. 10-181017 (1998), too, variations in resistance of power wires for the print head and variations in resistance of electrothermal transducers combine to produce errors. Further, if there is a large capacitor in the power wires, the voltage drop can vary widely depending not only on the current consumption at that instant but also on the immediately preceding current consumption, making the correction more difficult. Even with this drive system, it is currently not possible to provide a perfect correction.
As described above, in the conventional ink jet printing apparatus, the presence of power supply voltage variations normally makes it necessary to set the pulse width large enough to be able to supply a sufficient power for driving nozzles even when there is a supply voltage drop. The large pulse width in turn produces various problems, including increased power consumptions, large temperature rises in the print head, a shorter longevity of the print head, and burnt deposits on the heater degrading the ejection performance and the quality of printed images.
An object of the present invention is to provide an ink jet print head capable of stably and reliably driving an energy generation means such as heater at all times and also an ink jet printing apparatus having the same and an ink jet printing method.
In a first aspect of the present invention, there is provided an ink jet print head comprising:
a plurality of nozzles each having an electrothermal transducer to eject ink supplied into the nozzles when energized;
energization start means for start energizing the electrothermal transducers;
voltage detection means for detecting a voltage applied after starting the energization to the electrothermal transducers; and
energization stop means for stopping the energization of the electrothermal transducers according to the voltage detected by the voltage detection means.
In a second aspect of the present invention, there is provided an ink jet printing apparatus having an ink jet print head, the ink jet print head being adapted to print on a predetermined print medium by ejecting ink from a plurality of nozzles, the ink jet print head comprising:
a plurality of nozzles each having an electrothermal transducer to eject ink supplied into the nozzles when energized;
energization start means for starting energizing the electrothermal transducers;
voltage detection means for detecting a voltage applied after starting the energization to the electrothermal transducers; and
energization stopping means for stopping the energization of the electrothermal transducers according to the voltage detected by the voltage detection means.
In a third aspect of the present invention, there is provided an ink jet printing method for performing printing by ejecting ink, comprising the steps of:
starting energizing electrothermal transducers which generate thermal energy for ejecting ink;
detecting a voltage applied after the start of the energization to the electrothermal transducers; and
stopping the energization of the electrothermal transducers according to the voltage detected.
In the present invention with the construction described above, the time during which the energy generation means is energized is determined according to the actual voltage applied to the ink jet print head. That is, when the voltage applied to the electrothermal transducer is large, the time from the start to the end of the energization is set short. When the voltage applied to the electrothermal transducer is small, the time from the start to the end of the energization is set long. This enables an appropriate power to be supplied to the electrothermal transducer at all times, realizing a stable ejection of ink.
Further, in this invention, because the detected applied voltage is not fed back to the power supply, the apparatus can be constructed of a drive circuit with a smaller time constant than when a feedback circuit is additionally formed, thus eliminating such problems as oscillations during operation.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.